DE2142659B2 - DC-coupled limiter amplifier - Google Patents

Description

The invention relates to a DC-coupled limiter amplifier for linear amplification small signals and amplitude limitation of large signals, with a positive feedback branch for elimination unwanted interference phase modulations. In particular, it is an amplifier circuit with several in cascade, emitter-coupled differential amplifiers, in which the time delay the zero crossings of the angle-modulated signals are constant despite variations in the input signal level being held.

Limiter amplifiers are often used in FM receivers. The limiting effect is reduced unwanted amplitude modulations, noise interference and interferences related to the envelope of the frequency-modulated carrier wave may occur. However, the phase delay of the amplifier changes with the amplitude level of the signal so that amplitude modulations of the envelope are converted into phase modulations will. These phase modulations are then demodulated by the angle demodulator, so that in the output signal unwanted noise or interference appears.

Emitter-coupled differential amplifiers are often used as limiter amplifier stages in monolithic integrated circuits used. It is common practice to use these differential amplifier stages

vauisch to be coupled together, using an emitter follower stage as an intermediate stage. Such Limiter amplifiers have the disadvantage that they introduce a phase delay in what is to be amplified Introduce signal. This delay increases-

decreasing when the differential amplifiers are each controlled in their limiting state.

From the German Auslegeschrift 1 212 598 a multi-stage limiter amplifier is known in which A positive feedback branch is provided above each stage. These positive feedback branches are intended to increase of the input resistance if the limitation has not yet started, because the transistor input resistance in normal operation much lower than

In this way, the compensation of the delay-related input resistance changes due to the positive reverse phase modulation coupled with amplitude changes at the time of the stage can be traced back to the reduction of the input resistance. Decreased delay time due to the intended increase,
5 The invention uses a limiter amplifier coupling branch cannot be dimensioned in such a way that it gives a stage which, without positive feedback, causes the most valuable phase shift, since the signals carried for this purpose have a time delay that is inversely to the signal of the capacitor amplitude provided in the positive feedback branch. It is too big. Furthermore, a 10 stronger stage is provided for the input resistance increase aimed at in the known, a positive feedback over the entire circuit, so that the response time for switching on a resistor between the emitter input signals of low amplitude and the base of each amplifier transistor is practically the same, since the response time for signals of large amplitude is otherwise necessary make the relatively strong positive feedback into one.

lead to an intolerable tendency of the amplifier to oscillate. ₁₅ positions of exemplary embodiments explained in more detail.

It is also from the magazine "Radio Electronics" It shows

1968, pages 50 and 51 known, a multi-stage Fig. 1 is a circuit diagram of a first embodiment

integrated amplifier as a whole from its nature a limiter amplifier according to the invention,

output to its input for stabilization against Fig. 2 shows a representation of the phase delay

couple. ₂₀ over the signal amplitude for a compensated

The object of the invention is the sheep and an uncompensated limiter amplifier

function of a DC-coupled limiter server and

stronger, in which the positive feedback branch such a F i g. 3 the circuit diagram of a second embodiment level Phase shift is intended to ensure that the shape of the limiter amplifier according to the invention, phase shift introduced by the amplifier 25 in FIG. 1 are two limiter amplifier stages 500, is being canceled. This task is galvanically connected in series by 502 and in one the features specified in claim 1 solved. and the same integrated circuit 501 is shown.

In the case of limiter amplifiers, the individual limiter amplifiers are in certain

Type occur features built according to the state of the art.

1. With small signals much stronger signal 3 ° ^{So the} limiter amplifier stage 500 consists of the delays than with large signals and transistors 504, 506 and 508 and the resistors change ⁵¹⁰ > ^{512 and 514} · ^The bases of the transistors 504

2. Because of the limiting effect with increasing ^{and 506, the gain of the interconnection is connected to the} connections 532 and 534 ge signal amplitude, respectively. Their emitters are connected together and stärkers, so that the over the Mitkopp- ³ S are connected through a resistor 512 to a Anlungszweig fed back signal component to ^{circuit 536 (B} ~)> ^{the atlven with the ne} S terminal according to the change of the gain ^{of an} operating voltage source ß connected are also changed. This ^allows changes · ^The collectors of transistors 504 and 508 but also the influence of the back-coupled Hegen at terminal 530 (B +), so that these two signal and thus also connected in the amplitudenabhän- ⁴ ° transistors as an emitter follower. The phase shift of the amplifier korn connection 530 can be connected to the positive terminal of the pensoring phase shift of the voltage source ß. The collector amplifier fed and the fed back of ^the transistor 506 and the base of the transistor 508 signal combined input signal in the ^are connected together and have a desired way 45 resistor 510 at the terminal 530 (B +). The emitter of transistor 508 allows the input signal

Through the dimensioning according to the invention of the next limiter amplifier stage 502 and

These two effects are coupled via a resistor 514 to the connection 536

namely the phase delay of the amplifier and connected.

the phase lead brought about by positive feedback, so a terminal 534 becomes a practical bias Against each other. out which between the at the connections

Further developments of the invention are located in the voltages below 530 and 536. To the

claims. The input signal is applied to terminal 532,

The invention can be applied to a limiter which is superimposed on a quiescent equipotential

stronger with emitter-coupled differential amplifiers 55 essentially the same as that applied to terminal 534

use. The positive feedback (positive feedback) led voltage is.

results in a sufficiently large signal at low signal levels. Alternatively, connections 532 and 534

Amplification at which no oscillations are fed to even symmetrical input signals,

occur, but the output signal of the difference, each of which is superimposed on a bias voltage, which

stronger follows the input signal more quickly, so that ^fi o directly between the terminals 530 and

the time delay is reduced. When the voltages fed in 536 are present,

output signal becomes larger, the emitter-coupled The limiter amplifier stage 502 contains transi-

Differential amplifier in a symmetrical limiter 516, 518, 520 and resistors 522, 523, 524,

operation controlled, which eventually a full signal 525 and 526. The resistors 524 and 525 are in

limitation, so its gain 65 series between terminals 530 (B +) and 536

reduced (B-) with increasing input signal level. Your connection point is on the

will. This also reduces the gain of the positive base of transistor 518, which is softer than transistor comparisons.

Feedback with increasing input signal level. works more in the basic basic circuit. The basis of the

5 6

Transistor 516 is connected to the emitter of the transistor, i.e. transistors 516 and 518 (provided that

508 connected. The emitters of the transistors 516 that they according to the best practical execution

and 518 are interconnected and have the same DC bias voltages across the rungsform)

a resistor 523 at terminal 536 (B-). The times the load resistance, which mainly

Collectors of transistors 516 and 520 are also given by resistor 522. Normal

connected together to terminal 530 (B +), so this gain is low for signals

that these two transistors as emitter followers ar- level are quite large: voltage amplification

work. The collector of transistor 518 and the gene from 25 to 40. For low signal levels would

Base of transistor 520 are connected together with the effective capacitance of capacitor 550

and are multiplied by a factor of -25 to -40 via a resistor 522 at connection 10. Together

530. The emitter of transistor 520 provides the effect with resistor 510 can be

output signal to connection 554 and a signal is a significant phase lead for compensation

Resistor 526 coupled to terminal 536. sation of the phase delay, which

The values of the resistors 510, 512, 514, 522, otherwise by the series-connected

523, 524, 525 and 526 are typically in the 15 limiter amplifier stages at low signal levels

Order of magnitude of 1 kOhm for an integrated construction would occur.

wisely executed circuits. The collector-emit- With increasing signal level, the linear distribution

ter currents are then of the order of magnitude of the amplification range from the transistors 516 and

1 mA. Furthermore, the bases of the transistors 504, 518 formed differential amplifier stage for signal

506, 516 and 518 usually exceed a resting potential to a peak. There is therefore a limitation

led, which is half as large as the sum of the signal peaks on this, which are then no longer on

voltages across terminals 530 and 536. Output 554 appears. This reduces the

In such a case, resistors 510 provide voltage gain for these signals. The positive one

and 522 are best chosen so that they double the feedback is also reduced, and the

as large as the resistors 512 and 523 are. 25 Capacitor 550 causes a lower phase

Transistors 504 and 506, as well as leading current, form the base of transistor 508.

transistors 516 and 518 have an emitter-coupled device, but this is desirable because the delay of the am

th differential limiter amplifier. The transistor output of the differential amplifier signal occurring

508 is connected as an emitter follower and ensures that the input signal increases as it increases

Galvanic coupling between these two 30 signal levels is reduced. These two effects can

stronger levels. If no further measures are practically against each other through suitable dimensioning

are hit, then the leads are canceled by the transistors, so that the changes in the

516 and 518 formed emitter-coupled differential signal delay during signal transmission within

amplifier for signals of low level to a level below the limiter amplifier stage 502.

considerable signal delay. For signals higher 35 borrowed can be decreased.

Level, however, the signal delay is essential. The signal delay can be changed in the same way

less. within the limiter amplifier stage 500

A capacitor 550 with a small capacitance affects a positive feedback, which in the order of 1 picofarad connects the from the emitter of the emitter follower transistor 508 via the emitter of the transistor 554 to the base of the transistor 40 a capacitor 552 to one of the stage 500 vorgesistor 508. The Emitter follower stages is performed with the transient switched stage, not shown. which interfere with 508, 516 and 520 and which in basic reason - supplies the input signal at connection 532,
circuit-switched amplifier stages, for example with the positive feedback can also be used in other transistor 518. reverse the direction of the signals. Way as realized with the help of the capacitor 550 wehlche they amplify, not around. Hence the age of 45. For example, the collector of the feedback transistor 518, which is formed by means of the capacitor 550, can also regeneratively loop instead of via the capacitor 550 and thus forms a positive via a high-value resistor on the base of the or positive feedback. The parallel connection of the resistor transistor 508 can be performed. However, the state 510 with a capacitor would normally take up less space in an integrated circuit than a high resistance resistor because of the current integration property of the 50. Parallel capacitor causes a signal delay. The successor transistor 520 isolates the Konken. In this positive feedback circuit, the current capacitor 550 is from the collector load resistor 522. However, it flows through the capacitor 550 precisely in the direction that the capacitor 550 is in the opposite direction to the expected bandwidth and acts as a limited signal at the collector of the transistor 511 at the base of the transistor 508 Phase advance 55 is not restricted in an undesirable manner. A displacement current and not as a phase lag reduction of the bandwidth would be the edge current. Flatten the size of this phase advance of the limited signal and in this way the current depends on the voltage gain of a phase shift in the subsequent feedback loop. limiter amplifier stage, if such

The voltage gain of the positive feedback 60 is used. At the base of the transistor 5Of loop, on the other hand, a sufficiently high impedance acts from the emitter-coupled loop, which mainly determines the differential amplifier with the transistors 516 and 518 by the value of the resistor 510. The emitter follower with the transistors is tuned so that the capacitor 550 klcir 508 and 520 have a voltage gain which can be made. In this way it can only depend on the emitter follower effect and practically the positive feedback path to the base of the table equals 1. At low signal levels, the transistor 508 is connected to the base of the transistor 51 (amplification of the emitter-coupled differential connection. The impedance prevailing at the base of the Tran more closely equal to the product of half the forward partial transistor 116 is due to c '~

interfering 292 or 294 are connected and in this way form cascode amplifiers 280, 292 and 282, 294, which reduce the capacitive Miller effect in the differential amplifier 204. The collectors of the Transistors 292 and 294 are connected to a smoothed operating potential via resistors 296 and 298, respectively Emitter of transistor 238 connected.

The collectors of the transistors 238, 240 and are connected to the terminal T _n (B +).

lower. Emitter follower transistor 108 impedance low. If you would connect the capacitor 550 to the Connect the base of transistor 1.16, then you would need a much larger capacitor, to achieve the desired delay compensation.

The curve 402 in FIG. 2 shows the phase delay behavior a compensated limiter amplifier with several stages according to the invention

according to teaching. With full compensation the bases are also phase delay of a signal transmission stage via a resistor 288 via to the terminal T _n and via an avalanche diode a wide range of input signals relative to an avalanche voltage of 5.5 V to the ground constant. An optimal phase compensation for a connected in potential dc input signal. The cascade-connected signal transmission stages receives avalanche diode 286 is controlled by an operating current supplied via the Widerman when each subsequent stage stood at a level 15 288 in breakthrough in the limit, which operates a relatively constant delay so that it maintains the base voltage "^ Hi" results for each level.

F i g. 3 shows the circuit diagram of an IF limiter amplifier in an integrated design for FM receivers. This circuit diagram shows details of an integrated circuit for commercial applications. The high-gain IF limiter amplifier is normally designed in such a way that different ground reference points are selected for the input signals and the output signals. This avoids coupling the output signals to the input of the multi-stage limiter amplifier via the common impedance of a split ground reference line, which can lead to self-excitation or other undesirable behavior of the amplifier. In Fig. 3, the connections to the input signal reference ground are shown as a ground return symbol with four lines. This ground reference potential is fed from the integrated circuit 200 to the external circuit via the terminal T _n . The connections to the output signal reference mass are marked with a mass connection symbol in the form of a small triangle. This reference ground potential is fed from the integrated circuit 200 via the terminal T ₁₇ to the external circuit. A DC operating potential BH- of 8 to 16 V is fed to the integrated circuit 200 via the terminal T _u.

The angle-modulated input signals are transmitted to the integrated circuit die 200 via the Connections Γ., And T., from a matched transformer 202 fed out. The primary winding of the transformer 202 can carry the load of a preceding one. Form intermediate frequency amplifier, not shown.

The IF limiter amplifier according to FIG. 3 has three balanced differential limiter amplifiers coupled together 204, 206 and 208. The first differential amplifier 204 includes transistors 280 and 282, the emitters of which are connected together and connected to the collector of a transistor 210. The second Differential amplifier 206 includes transistors 305 and

307, whose interconnected emitter is connected to the transistor 292 and 294, respectively. The emitter collector of a transistor 212 is led. The 60 of the transistor 205 is connected to the base of the transistor third differential amplifier 208 contains transistors 307 and is connected to the input signal reference potential via a resistor 300 326 and 328. The emitter d leads to the collector of a transistor 214. Transistor 207 is connected to the base of transistor 3o!

The bases of transistors 280 and 282 of the first are connected and across a resistor ^ n? Differential amplifiers 204 are connected to the input terminals 65 at the input signal reference potential. The KoIIeVt circuits 7 "., Or T _n connected. The collectors of transistors 205 and 207 are Witte / ■ * · T of the transistors 280 and 282 are connected to the emitters of 304 and 306 to the terminal T (B +) to St.

Basic basic circuit of switched amplifier transitions. These resistors are relatively low-7

309581/362

so that it smooths and regulates the base voltage for transistors 238, 240 and 242. the The emitter voltages of these three transistors are approximately 4.8 V.

The base biases of transistors 292 and 292 and transistors 210, 212 and 214 become supplied by a series connection of the following elements:

1. a resistor 272 connected between the emitter of transistor 238 and the Bases of transistors 292 and 294 is connected,

2. a resistor 274, which between the connected Bases of transistors 292 and 294 and the connection point of the bases of transistors 210, 212 and 214 are switched is and

3. A series connection of a forward biased diode 276 with a resistor 278, which between the interconnected bases of the transistors 210, 212 and 214 and the input signal ground potential is switched.

The transistors 210, 212 and 214 are with their

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Input signal ground reference potential switched. The collector currents of transistors 210, 212 and 214 are kept constant. The base voltages of transistors 210, 212 and 214 become 1V above of the input signal reference ground potential, the diode 276 fluctuations in the Compensates base-emitter junction voltages of these transistors and temperature fluctuations.

The voltage appearing at the base of the transistor 210 is fed via a line 608 to a further, not shown bias source for the integrated circuit led as a reference voltage is used for control circuits, also not shown, and voltages and currents for other parts of the integrated circuit 200 supplies.

The transistors 205 and 207 work as emitter followers. Their bases are attached to the collectors of the Tran

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cause attenuation of harmonics which occur at the base of a subsequent transistor 346 and rapid signal transitions in the emitter follower with the emitter of this transistor 346 via a transistors 205 and 207 . Resistor 350 is connected. The collectors of the

The emitter of the transistor 207 is connected to the co-transistors 349 and 346 via resistors 340 coupling capacitor 310 to the emitter of the 5 and 342 to the terminal T ₁₄ . Connected to this transistor 294. The emitter of the way is a Darlington circuit 230 , transistor 205 is connected to a positive feedback connector which works as a voltage follower and output converter 312 at the emitter of transistor 292. The signals at terminal 234 supplies, which with positive feedback capacitors 310 and 312 of the positive emitter of the transistor 346 is connected. The emitting feedback branch couple the signal with io ter of this transistor is also connected via the rows of the same phase position as the original input circuit of resistors 356 and 358 to the signal back to the emitter of the transistors 294 output signal ground potential. The or 292. This positive feedback controls the junction of resistors 356 and 358 signal transitions. The tendency for the second difference lies across a resistor 360 at terminal T ₃ . Limiter amplifier stage 206 for the introduction of 15 The base of the transistor 282 of the first amplifier phase shifts of the output signal, which stage 204 is at the terminal T _s .
are dependent on the input signal level, this will In the same way is the collector of the transistor

degraded. The reason for this is that the 328 connected to the base of the transistor 336 , signal transitions for all input signal levels, and its emitter to the base of a subsequent not only for high input signal levels, quickly followed by transistor 338 and via a resistor 348 . the emitter of this transistor is performed. The Collective

The collectors of transistors 305 and 307, the gates of the transistors 336 and 338 are reflection stage 206 are connected through resistors 218 and 220 to stands 332 and 334 to the terminal T ₁₄ (6 ', -) reasonable geeine regulated and smoothed operating voltage leads . In this way, a Darlington circuit formed by the emitter of the transistor 240 25 device232, which is delivered as a voltage follower. The connected emitter provides output signals at connection 236 , which is connected to the differential amplifier transistors 305 and 307 to the emitter of transistor 338 . A ner from the collector of transistor 212 is the emitter of this transistor via the series constant bias current. connection of resistors 352 and 354 to the

The transistor 209 serves as an emitter follower, its output signal ground potential. The common base is connected to the collector of the transistor 305, the connection point of the resistors 352 and 354 . Its emitter is at the base of the transistor via a resistor 362 to the terminal T ₁ sistor 326 of the third amplifier stage 208 and is guided. The terminal T ₄ is galvanically connected via the SC via a resistor 324 to the input signal secondary winding of the transformer 202 (which is connected to outside ground potential. 35 is provided half of the integrated circuit 200 )

The transistor 211 also works as an emitter to the terminal T ₂ , which is connected to the base of the tranfollower and has its base connected to the collector of the transistor 280 of the first limiter amplifier stage 204, transistor 307 . Its emitter is connected to. A tuning capacitor is drawn over this winding in the figure of the base of transistor 328 of the third amplifier,
stage 208 and is connected via a resistor 322 to the 40 A also outside the integrated Schuiumg input signal ground potential. The 200 arranged signal bridging capacitor collectors of the transistors 209 and 211 are coupled via the terminals T _s and T ₄ with each other, so resistors 318 and 320 are connected to the terminal T ₁ , (B-f) that the obtained in differential amplifier operation. IF signals from outputs 234 and 236 via

The emitter of transistor 209 is counteracted by a 45 resistor networks 352, 354, 362 or 356, 358, positive feedback capacitor 314 to the collector of 360. This counteracting transistor 292 is connected. The emitter of ken prevents these IF signals again lies on the transistor 211 via a Mitkopplungskon.- the bases of transistors 280 and 282 of the gear 316 Eindensator amplifier stage 202 arrive at the collector of transistor 294.. The rest in the third differential Begrenznngsverstärkerstufe 208 corresponds to state differential amplifier signals occurring wcrhält transistors 326 and 328, the emitters of the inlet, however, degenerative recycled and are stabilisammengeschaltet and a constant current Sieren the bias voltages of the collector of the transistor 214 Differenzverstärkervom obtained. The load stages 204, 206 and 208 within the negative feedback resistors 222 and 224 lead the collectors of the loop. To bridge the connections T ₁ transistors 326 and 328 to a regulated and 55 and T ₄ to ground potential, additional cone-smoothed operating voltage, which is used at the emitter of the capacitor.
Transistor 242 prevails. The collectors of the tran- In operation there is one above the secondary winding

Transistors 326 and 328 are connected together via the input signal connected in antiparallel with the transformer 202, second diodes 226 and 228 . The "e see the bases of the transistors 280 and 282 de <diode antiparallel connection provides a limiter 60 differential amplifier 204 coupled, which acts when the signal transition between the transistors 292 and 294 to a cascode connection: signal peak voltages between the two collectors are. As a result of these cascode inputs, transistors 326 and 328 reach 1.3V. This limiting effect occurs for lower one-collector-base capacitance of transistors 280 and output signal level. 1 than the limiting effect of 65 282. This increases the input impedance of the first limiter amplifier 208 itself. Difterential amplifier stage 204 increases and remains prak

The collector of the transistor 326 is constant at the base table when the stage in the limiter is connected to the transistor 349 , the emitter of which is controlled with stand.

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The signal appearing at the collectors of transistors 292 and 294 has been delayed in phase in transmission through transistors 280, 292 and 282, 294. The signal is then transmitted via the emitter follower transistors 205 and 207 to the bases of the transistors 305 and 307, respectively, of the second amplifier stage 206 with a minimal additional phase shift which depends on the amplitude of the signal.

The feedforward capacitors 310 and 312 are selected so that the phase lag of the first signal transmission stage 204 is compensated for at low signal levels. Capacitors 310 and 312 have small capacitance values, typically on the order of 1.3 pF. The gain of this feedback path is kept smaller than 1, so that no oscillations occur. In the first amplifier stage 204 , the positive feedback is fed to the emitters of the transistors 292 and 2 ° 4 so that the high input impedance at the input connections T ₂ and T _{3 is} not impaired.

Application of the principles of the invention to balanced amplifiers as opposed to single-ended amplifiers as shown in FIG. 1 is explained in connection with the second differential limiter amplifier stage 206 . The positive feedback from the output to the input takes place via the positive feedback capacitors 314 and 316, which are connected to the bases of the emitter follower transistors 205 and 207 instead of to the bases of the transistors 305 and 307 , because the bases of the transistors 205 and 207 have a higher and therefore more favorable impedance level provide for the return of these capacitors. In this way, capacitors 314 and 316 can have significantly smaller capacitance values, typically on the order of 0.27 pF, to compensate for the phase delay introduced by the second amplifier run 206. However, capacitances with such low values can be formed relatively easily in integrated circuits.

When the limiting level of the second amplifier stage 206 is reached, then the effect of the positive feedback diminishes progressively, since the gain of the stage 206 is progressively reduced when the limiting is reached, ie the input signal of this stage increases but the output signal remains constant. Therefore, the contribution capacitors do not have their maximum effect for small signals, where they significantly reduce the delay introduced by the first and second amplifier stages 204, 206 , on the other hand they have a negligible effect when the input signals rise to a level at which the second stage 206 is full limited and the phase lag is reduced.

The invention can be used in circuits both for balanced signals and for unbalanced signals Apply signals.

The third amplifier stage 208 operates in the same way as the second amplifier stage 206. In the third stage 208 , no positive feedback capacitors are used. The signal amplitudes appearing at the bases of the transistors 326 and 328 have been amplified by the first and the second amplifier stage 204 and 206 , respectively. The signal amplitude is therefore large enough to control the third stage 208 for all signal levels occurring at the input connections T ₁ and T ₃ in the limiting state.

The third amplifier stage 208 is provided with a further limiter which comprises the diodes 226 and 228 connected in anti-parallel and connected between the outputs. They allow the output signal peak amplitude to be limited to about 1.3 V. The signals at the outputs of the third amplifier stage 208 are each fed via Darlington emitter follower transistors to the subsequent circuit, which is presented with low source impedances in this way. The emitter loads of the Darlington emitter followers are each galvanically led via feedback branches to the corresponding input connections T ₂ and T ₃ for DC voltage stabilization of the limiter amplifier circuit.

1 sheet of drawings

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Claims (9)

Patent claims: 1. DC-coupled limiter amplifier for linear amplification of small signals and amplitude limitation of large signals, with a positive feedback branch to eliminate unwanted interference phase modulations, characterized in that to compensate for the amplitude-dependent phase shift between the output signals and the input signals of the degree of positive feedback with regard to the gain of the amplifier with regard to its phase rotation is dimensioned that for signals with fluctuating amplitude, such as signals lying below the limit level, the phase lead of the fed back signal caused by the positive feedback branch (550, 510;) is equal to the phase delay occurring in the amplifier for these signals. 2. Limiter amplifier according to claim 1, characterized in that it contains a first and a second transistor (518, 516; 307, 305) in an emitter-coupled differential amplifier circuit (502, · 206) , in which in the collector circuit at least the first transistor (518; 206 ) a resistor (522; 220) is provided that the feedback branch contains a third transistor (520; 211) in a first emitter follower circuit, the base of which is connected to the collector of the first transistor (518; 206) , and the emitter of which is connected via a first Impedance (550; 316) is coupled to the base of the second transistor (516; 305) , and that between the base-side end of the impedance (550; 316) and a DC voltage potential (B +) a first resistor (510; 298), which Input signal currents can be supplied, is switched on. 3. Limiter amplifier according to claim 2, characterized in that the base-side end of the first impedance (550; 316) is connected to the base of the second transistor (516; 305) via a second emitter follower (transistor 508; 207) . 4. Limiter amplifier according to claim 2, characterized in that the differential amplifier (206) has a load resistor (218) in the collector circuit of the second transistor (305), that in addition a positive feedback branch with a third emitter follower (transistor 209) is provided, which with his The base is connected to the collector of the second transistor (305) , and from the emitter of which a second impedance (314) is led to the base of the first transistor (307) , and that a second resistor (296) between the base-side end of the second impedance (314 ) and the DC voltage potential (B +) is switched. 5. Limiter amplifier according to claim 4, characterized in that the base-side end of the second impedance (314) is led via a fourth emitter follower (transistor 205) to the base of the first transistor (307) . 6. Limiter amplifier according to claim 3 or 5, characterized by a first preamplifier transistor (506; 294) operated in a basic basic circuit, the collector of which is connected to the base of the first emitter-follower transistor (508; 207) , of the emitter of which a first capacitor (552; 310) is connected to the input of the first preamplifier transistor (506; 294) . 7. Limiter amplifier according to claim 6, characterized by a second preamplifier transistor (292) operated in a basic basic circuit, the collector of which is connected to the base of the fourth emitter follower transistor (205) , from the emitter of which a second capacitor (312) is connected to the input of the second preamplifier transistor (292) is switched. 8. Limiter amplifier according to claim 2, characterized in that the first impedance (550; 316) is capacitive. 9. Limiter amplifier according to claim 4, characterized in that the second impedance (314) is capacitive.